Since I use this diving board I'll start here. Can you reasonably age coral by measuring it? More specifically I need to do the equivalent of the newspaper front page documentation. ...these corals can be this old, but no younger than...

Can you age a wreck by measuring some of the coral growing on it, or what I am trying to attempt, determine if two wrecks sank roughly at the same time? The two wrecks are within 4 miles of each other.

Is there a specific type of coral or other life form(s) that grow in the Caribbean to use? I would photograph similar organisms with a measuring device held close but not in any way that would damage it at both sites. Both would clearly have to be growing on the wreck.

you can age corals from their size, but the accuracy would not be there - unless you start taking cores of the coral (examine the layering of their skeleton and chemical make up). Many corals grow at known rates (plenty of scientific literature out there detailing coral growth rates). However, a word of warning - many of the growth rates are site/species specific - as many biological (predation, competion etc) and physical (water temperaure, light avaliability, sediment load etc) factors can influence the growth of corals. You could make a rough judgement - but it would be rough. Hope this helps. You could try contact a research group in the area you are interetsed in - as they would probably be able to point you in the right direction - of either papers or actual data.

I agree with acroporas, you should measure rust thickness in similar areas of the two wrecks, sedimentation might work but it might depend a lot on local currents. In acroporas's graph, its hard to make a real case without the error bars.Bill

You probably should be looking at more predictable things such as the extent of rust/decay or the ammount of sedimentation.

But if you want to do it by measureing the size of coral, you might be able to modify a growth rate experiment I did to suit your needs.

I measured the size of a bunch of colonies of Acropora tenuis. I then looked at the frequency of different sized colonies.

As you can see, there is a peak in frequency every 5 cm or so. Knowing that in this species spawning is a yearly event, I concluded that the coral was growing about 5 cm a year.

You could then use that growth rate to calculate the age of the largest colonies. Count colonies on both wrecks and you can correct for differences in growth rates on the different wrecks

Or if the pattern continues all the way back to the largest (oldest) collonies you can count the number of peaks (years) directly.

We ran an experiment where we setteled the planula of two species of coral and monitered their growth under the same lab conditions (open system) for a year and there still was a lot of variation in size.

To add to the growth conundrum, aging a colony that at the genetic level may never senesce (age) would be difficult. Size would give a relative age since settlement like others have said, but fragmentation is also a means of reproduction especially with some species of acropora. This would cause problems in aging a colony.